Modern information systems require a high speed data transmission. Fiber optical systems provide a high bandwidth and are widely use in communication systems. Fiber optic bundles are commonly utilized in fiber optical systems to increase the communication bandwidth. Many methods of creating fiber bundles exist. They include crimping, tie cables, insertion of fibers into ferrules, etc. Of particular interest are the efforts to reduce fiber-to-fiber pitch because many applications require or benefit from fiber bundles having a small fiber-to-fiber pitch. For example, a liquid crystal beam steering-based 1×6 fiber optical switch, which inherently utilizes a small steering angle, requires fiber bundles with fiber-to-fiber pitch of 50 μm or less to operate. In another example, in MEMS (Micro Electronic Mechanical System) micromirror-based switch, the beam deflection angle is proportional to micromirror's tilt angle. A fiber bundle with smaller fiber-to-fiber pitch requires a smaller micromirror tilt angle which would reduce driving voltage, thus increasing system's reliability and reducing its power consumption.
Another example is a fiber coupler (such as power monitoring tap coupler), that couples light from one fiber to other fibers. In a fiber coupler assembly, a lens is usually used to couple the light into fibers. A fiber bundle with reduced fiber-to-fiber pitch results in fibers being closely packed at the optical axis of the lens which improves device's coupling efficiency.
Circulators, variable optical attenuators, wavelength selective switches, reconfigurable optical add/drop modules, chromatic dispersion compensators, etc. also benefit from utilizing fiber bundles with reduced fiber-to-fiber pitch.
Typical single mode fibers have an inner core (active area) diameter of about 9 micrometers (μm) and an outside diameter of 125 μm. In order to produce a fiber bundle with a reduced fiber-to-fiber pitch, the fiber outside diameter has to be reduced.
A reduction of the outside diameter of the fibers also results in an increase of the packing fraction of the fiber bundle, which is defined as the ratio of the information-carrying cross-sectioned area of the fiber bundle (fiber cores) to the total cross-sectioned area of an endface of the fiber bundle. The increased packing fraction of the fiber bundle is beneficial for applications where increased density of light is important.
A method of reducing fiber outside diameter is disclosed in the U.S. Pat. No. 3,912,362 to Hudson, hereinafter referred to as '362 patent. The '362 patent discloses fiber bundle termination where fibers are etched and inserted into a ferrule and secured to each other and the ferrule by adhesive. The '362 patent discloses fibers with an inner active core having a large diameter. The inner core diameter of processed fibers disclosed in '362 patent is 3.6 mils, which is equivalent to about 91.4 μm, and an outer diameter of those fibers equal to 5.5 mils (139.7 μm). The '362 patent teaches etching the fibers to reduce the outer diameter to 3.8 mils (96.5 μm). Because the after-etch diameter of the fibers was still very large, fiber breakage was not a concern, and special means to prevent breakage of the fibers were not required.
Accordingly, a need exists to create a fiber bundle with a fiber-to-fiber pitch smaller than 50 μm for fibers having small inner core diameter, typically in the range of about 3.5 μm to about 10 μm. That requires the after-etch fiber outside diameter of less than 50 μm. Fibers with small outside diameter are extremely fragile and are very difficult to handle. This problem is overcome by the hereinafter disclosed fabrication method that stabilizes the fibers and reduces the possibility of breakage associated with a small after-etch fiber outside diameter.